Thermal switch



Aug. 22, 1961 w WAY, JR 2,997,562

THERMAL SWITCH Filed May 25, 1960 IN V EN TOR.

, lrrozA/a'Y United Smtes Patent 2,997,562 THERMAL SWITCH William H. Hathaway, Jr., 773 Mayfield Ave., Norfolk 3, Va. Filed May 25, 1960, Ser. No. 31,770 1 Claim. (Cl. 200-442) This invention relates to an electrical switch device, and it particularly relates to a switch device which incorporates a thermal element to make the switch thermally responsive.

There are many different types of application where it is highly desirable to control an electric circuit in accordance with thermal changes in the environment. An example of this is the problem of protecting motor shaft bearings.

Motor shaft bearings are a vital part of a motor and any damage to these bearings will often seriously damage the motor itself because of the intense heat generated by the consequent friction.

In order to control electrical circuits Where a sudden build-up of thermal energy will cause serious damage, various different types of thermal switch means have heretofore been proposed. However, these prior devices were generally unduly complicated and once they were tripped, they required considerable skill and efiort to be reset. Often, the entire switch had to be removed from its circuit, completely disassembled in order to replace the thermal element, and then reassembled prior to being replaced in the circuit. ln addition, some of these prior switch means were subject to all the environmental con ditions, such as pressure, moisture, dirt, dust, etc., to which the controlled environment was itself subject. As a result, there was a great tendency for breakdowns and clogging of the parts of the switch.

it is one object of the present invention to overcome the above as well as various other disadvantages of the prior art by providing a thermal switch for electrical circuits which requires manual re-setting after it has been tripped but which can be easily and quickly re-set without disassembling it completely or removing it bodily from its environment.

Another object of the present invention is to provide a thermal switch of the aforesaid type which is relatively simple in construction and which is not readily subject to breakdowns and faulty operation.

Other objects of the present invention are to provide an improved thermal switch, of the character described, that is easily and economically produced, which is sturdy in construction, and which is highly efiicient in operation.

With the above and related objects in view, this invention consists in the details of construction and combination of parts, as will be more fully understood from the following description, when read in conjunction with the accompanying drawing in which:

FIG. 1 is a sectional view of a switch device embodying the present invention, the switch device being shown applied to a motor shaft bearing.

FIG. 2 is a top plan view taken on line 22 of FIG. 1.

FIG. 3 is a cross-sectional view taken on line 3-3 of FIG. l.

FIG. 4 is a cross-sectional view taken on line 44 of FIG. 1.

FIG. 5 is a cross-sectional view taken on line 55 of FIG. 1.

Referring in greater detail to the drawing wherein similar reference characters refer to similar parts, there is shown a thermal switch device, generally designated 10, comprising an upper metal housing 12 and a lower metal housing 14. The two metal housings 1'2 and 14 are separably connected, with the lower housing 14 being ice secured in position on the environment to be controlled, in this case the bearing 16 of a motor shaft 18, while the upper housing 12 is readily removable from the lower housing 14 without removing the lower housing 14 from the shaft bearing 16.

The upper housing 12 comprises a generally cup-shaped chamber 20 having a hollow interior and an open top. The open top is defined by internal threads 22 which are adapted to be threadedly engaged with an externally threaded plug 24 having a top peripheral flange 26 adapted to seat on the upper peripheral edge of the chamber 20 when the plug 24 is screwed in place (as shown in FIG. 1).

The plug 24 is made of electrically insulative material such as phenolic resin or the like, theplug 24 serving as a support for a'pair of electrical contacts 28. These contacts 28 are pins having threaded upper portions and unthreaded lower portions, these lower portions forming contact points 30. The threaded upper portions of the pins 28 extend through respective drilled and tapped bores in the plug 24 and the upper ends of these pins project above the top of plug 24. These upper ends form terminal posts and are each provided with a pair of nuts 32 to releasably secure an electrical lead wire to the posts. The pins 28 are retained against longitudinal movement by the nuts 32 in one direction and by flanges or washers 34 in the other direction.

The plug24 is provided with an up er central boss 36 which defines the upper end of an elongated recess 38 on the inner side of the plug 24. Into this recess 38 extends the upper end of a rod 40. This rod 40 is provided with a flange or washer 42 which underlies an electrically insulative disc 44, the *disc 44 being preferably constructed of fibre. The disc 44 is drilled and tapped at its central portion to threadedly engage with a threaded portion 46 on the rod 40.

The disc is provided with an annular groove or recess on its upper surface and in this groove is seated a ring or washer 48 constructed of electrically conductive material and positioned to be engaged by the contact points 30. The ring 48 is biased away from the contact points 30 by means of a coil spring 50, this spring 50 encircling the rod 40 and being positioned between the disc 44 at one end and a shoulder formed by a counterbore S2 in the underside of plug 24.

The chamber 20 of the housing '12 is provided with a central aperture at its lower or closed end and this aperture mates with a central bore 53 in an externally threaded nipple 54 integral with and formed of the same material as the chamber 2%. The rod 40 extends through the aperture in the chamber 20 and through the bore 53 in the nipple 54 into an axially aligned bore 55 in the housing 14 (as shown in FIG. 1).

The housing 14, constructed of heat conductive material, includes a top nut portion 56 of hexagonal shape for easy grasping by a wrench or the like. From the nut portion 56 depends an integral nipple 58 in which the axial bore 55 is located to mate with a counterbore in the nut portion 56. This counterbore is internally threaded to engage with the external threads on the nipple 54 whereby the upper housing 12 is releasably engaged with the lower housing 14.

The nipple 58 of the lower housing 14 is externally threaded for engagement with a tapped hole in the housing 60 of the bearing 16. At its lower end, the nipple 58 is provided with an extension 62 which is hollow to mate with the hollow or bore 55 within the nipple 58.

Within the extension 62 is provided a removable cartridge 64 within which is provided a thermal plug 66 made of tin and lead alloy having a melting point of about F. The thermal plugs material may vary in accordance with the desired melting point or other desired characteristics. However, it is essential that the thermal plug melt at whatever temperature equals the maximum temperature desired as a control point.

The rod 40 extends through the nipple 58 and the lower end of the rod abuts against the plug 66. This abutment provides a stop or counter-pressure against the force of spring 50 whereby the contact ring 48 is held in engagement with contact points 30 as long as the plug 66 remains in the solid state. However, when suflicient heat energy has been generated by friction. or other means in the bearing 16, the plug 66 will melt and the spring 50 will thereupon immediately force the disc 44 and contact ring 48 away from the contact points 30 to open the circuit. The downward movement of the rod 40 will be limited by the flange or washer 42 abutting against the lower wall of the chamber 20.

In order to re-set the switch after the above-described operation, it is merely necessary to unscrew the nipple 54 from the countrebored nut portion 56 of the lower housing 14 and remove the upper housing 12 from the lower housing 14. Then the cartridge 64 is removed and a new cartridge is substituted. Thereafter, when the upper housing 12 is replaced into engagement with housing 14, the device is set for further use.

Although the resetting of the device is simple and readily accomplished, it should be noted that it still requires a positive manual effort to reset the switch. This insures against the possibility of the switchs r e-setting itself before the trouble is traced and rectified.

Although this invention has been described in considerable detail, such description is intended as being illustrative rather than limiting, since the invention may be variously embodied, and the scope of the invention is to be determined as claimed.

Having thus set forth and disclosed the nature of this invention, what is claimed is:

A thermal switch assembly comprising a lower metallic cup-shaped housing, an externally threaded nipple integrally depending axially from the bottom of said housing, said nipple having a small bore extending axially thereof and ending at a closed bottom in said nipple, a replaceable open top cartridge in said bottom end of said nipple bore, a meltable thermal element in said cartridge,

said nipple being externally threaded for mounting it in a desired location to be protected, said lower housing having an external shape facilitating threading said nip ple into the desired location, said lower housing having a threaded large counterbore therein axially aligned with said nipple small bore, an upper cup-shaped housing, an axially bored nipple axially depending integrally from said upper housing, said upper housing nipple being externally threaded complementary to said lower housing threaded counterbore and detaohably secured thereto, a peripherally threaded cover for said upper housing, said cover being of insulating material, a peripherally extending flange on said cover, complementary threads in said upper housing for securing said cover to close said upper housing with said cover flange extending thereagainst, an axial recess extending into said cover from the bottom thereof, a pair of diametrically spaced contact pins extending through said insulating cover, a rod extending through said axially aligned recess and nipple bores and resting with one end on said meltable element and its other end extending into said cover recess, a flange on said rod, said rod flange being Within said upper housing, an insulating disc having an upper annular recess threaded onto said rod against said flange thereon within said upper housing, a conducting ring mounted in said disc annular recess, said rod when in contact with said meltable element, when unmelted, supporting said conducting ring in tight elecrtical contact against both said spaced apart contact pins, and a coil spring about said rod biased be tween said insulating disc and the bottom of said cover urging said insulating disc and said contact ring therein away from electrical contact with said contact pins to interrupt a circuit therethrough when the meltable plug is melted.

References Cited in the file of this patent UNITED STATES PATENTS 1,875,928 Lovekin Sept. 6, 1932 2,023,377 Werring Dec. 3, 1935 2,066,632 Lovekin et al. Jan. 5, 1937 2,272,978 Knaack Feb. 10, 1942 2,749,409 Kay June 5, 1956 

